[{answers:{"question1":"a","question2":"c","question3":["a","b"],"question4":1},createdAt:ISODate("2022-03-04T07:30:40.517Z")},{answers:{"question1":"b","question2":"c","question3":["a","c"],"question4":2},createdAt:ISODate("2022-03-04T07:30:40.518Z")}]

db.collection.aggregate([{$project:{"answers":{$objectToArray:"$answers"},"date":{$dateToString:{format:"%Y-%m-%d",date:"$createdAt"}}}},{$unwind:"$answers"},{$unwind:"$answers.v"},{$group:{_id:{answers:"$answers",date:"$date"},c:{$sum:1}}},])